Power train for pumps, energy generation systems or similar and method for starting up a power train of this type

ABSTRACT

Disclosed is a power train including a drive shaft of a working machine, a drive machine and a differential gear with three drives or power take-offs, wherein one power take-off can be connected to the drive shaft, a first drive can be connected to the drive machine and a second drive can be connected to the differential gear. One drive can be connected simultaneously to the other drive or to the power take-off.

The invention relates to a power train with the features of the preambleof claim 1.

The invention relates furthermore to a method for starting up a powertrain with the features of the preamble of claim 25.

A general problem of driven machines, such as conveyor apparatuses, forexample pumps, compressors and fans, or such as pulverizers, crushers,motor vehicles, etc., is efficient, variable-speed operation or startingup under load, or operation of, for example, energy extractioninstallations up to a speed equal to zero. Furthermore, electricalmachines are used as an example of drive machines or generators, but theprinciple applies to all possible types of drive machines, as well asto, for example, internal combustion engines.

The electrical drives and generators that are most frequently used atpresent are three-phase machines, such as, for example, asynchronousmachines and synchronous machines that are operated essentially onlywith constant speed. Moreover, a three-phase machine and a networkdownstream of it must be designed to be correspondingly large so thatthey can deliver a desired driving torque from a standstill. Therefore,electrical machines for this reason will also instead be connecteddirectly to a power system, often made in combination with a frequencyconverter as a variable-speed drive. Thus, variable-speed operation fromspeed zero can be implemented without heavily loading the power system,but the approach is expensive and linked to major efficiency losses. Onemore economical alternative that is better in comparison and also betterin efficiency is the use of differential systems—for example accordingto AT 507 394 A. The basic limitation here is, however, that dependingon the transmission ratio of the differential stage, only a relativelysmaller speed range can be achieved, and therefore in the so-calleddifferential mode, i.e., in the case of the speed changes using thedifferential drive at the operating speed of the drive machine,essentially lower speeds on the drive shaft of a driven machine cannotbe achieved.

There are several possibilities for doing this. According to DE 20 2012101 708 U, for example, the transmission ratio of the differential gearcan be fixed at 1. On this basis, the complete power train can be drivenwith the differential drive or the drive machine can be brought tosynchronous speed and can be subsequently synchronized with the powersystem.

The disadvantage of this approach is that the differential drive and thefrequency converter downstream of it are dimensioned to be much smallerthan the drive machine and therefore can also only deliver acorrespondingly small torque. This is not enough to accelerate the drivemachine to the synchronous speed when the driven machine is inoperation.

AT 514 396 A shows an approach with which drive machines can beaccelerated into a speed range with high torque and the driven machinecan be started up in a further step away from speed zero. This is doneby the drive machine being started up from a speed of zero or roughlyzero while an external braking torque acts on the drive shaft, and bythe second drive being braked in an acceleration phase of the driveshaft. The disadvantage of this approach is that the braking device thatis necessary for this purpose is complex and with a differential drivein a size on the order of, for example, 20% of the total system output,only a continuous speed range of roughly 50% to 100% of the workingspeed can be implemented.

The object of the invention is therefore to find an approach with whichdrive machines can be accelerated preferably under load, for example inorder to synchronize with the power system electrical machines coupled,for example, directly to a power system, and a large working speed rangecan be implemented.

This object is achieved with a power train with the features of claim 1.

This object is furthermore achieved with a method with the features ofclaim 25.

The heart of a differential system is a differential gear that in asimple embodiment can be a simple planetary gearing stage with threedrives and power take-offs, one power take-off being connected to thedrive shaft of a driven machine, a first drive being connected to adrive machine and a second drive being connected to a differentialdrive. Thus, the driven machine can be operated in a variable speedmanner at constant speed of the drive machine, the differential driveenabling a variable speed of the drive shaft.

In order to start a driven machine from a standstill, and if the drivemachine is an electrical machine, additionally to bring a drive machinefrom a standstill preferably to synchronous speed, the system can beoperated according to the invention, for example, in the following threephases:

Phase 1: A differential drive is connected at a standstill both to thefirst drive and also to the second drive of the differential system.Then, the differential drive is accelerated, and the driven machinebegins to work. Depending on the torque characteristic of the drivenmachine and the output of the differential drive, in this operating modeI preferably a working speed range of up to roughly 40%-50% of thenominal working speed of the driven machine is implemented. The drivemachine remains in this operating mode I separated from the powersystem. The transmission ratios of the gear stages via which thedifferential drive is connected to the two drives are preferably chosensuch that the drive machine at least approximately reaches its operatingspeed as soon as the differential drive enters the vicinity of its powerlimit. The differential drive works in the motor mode in thisphase—i.e., it takes power from the power system.

Phase 2: The drive machine that is connected to the first drive of thedifferential system and that is now running in the operating speed rangeis connected to the power system at this point. Since the differentialdrive works in the generator mode in the lower working speed range ofoperating mode II—i.e., it delivers power into the power system—in thenext step the torque of the differential drive is adjusted from themotor mode into the generator mode. In this way, the drive machine iscontinuously more and more heavily loaded until the entire differentialsystem preferably enters the region of the lower limit of the workingspeed range of operating mode II.

In order to keep the system loads as small as possible, preferably thetransition from the motor mode to the generator mode of the differentialdrive takes place damped, i.e., not suddenly.

Phase 3: As soon as an operating point in the lower working speed rangeof operating mode II has been set on the differential drive and on thedrive machine with respect to speed and torque, the differential driveis separated from the first drive of the differential system. The systemnow works in the differential mode with which in this third phase forthe driven machine, a maximum torque at maximum driving speed can beimplemented.

Preferred embodiments of the invention are the subject matter of thedependent claims.

Preferred embodiments of the invention are explained below withreference to the attached drawings. Here:

FIG. 1 shows the principle of a differential system for a drive of apump according to the state of the art,

FIG. 2 shows an embodiment of a differential system according to theinvention for high-speed drives,

FIG. 2a shows a diagram with a typical torque characteristic of a pump,

FIG. 3 shows another embodiment of a differential system according tothe invention for high-speed drives,

FIG. 4 shows a time characteristic of the speed parameters and powerparameters of a differential system during start-up,

FIG. 5 shows an embodiment of a differential system according to theinvention for slow-speed drives,

FIG. 6 shows another embodiment according to the invention, in which adifferential drive can be connected to a second drive and a powertake-off of a differential system,

FIG. 7 shows another embodiment according to the invention, in which adifferential drive 5 of a differential system is connected to the seconddrive and can be connected to the power take-off,

FIG. 8 shows another embodiment according to the invention, in which adifferential drive 5 of a differential system is connected to the seconddrive and can be connected to the power take-off,

FIG. 9 shows another embodiment according to the invention, in which apower take-off can be connected to a first drive of a differentialsystem,

FIG. 10 shows another embodiment according to the invention, in which adifferential drive can be connected via a second drive to a first driveof a differential system,

FIG. 11 shows an embodiment of a differential system according to theinvention with a positive gear,

FIG. 12 shows another embodiment of a differential system according tothe invention with a positive gear, and

FIG. 13 shows another embodiment of a differential system according tothe invention for an energy extraction installation.

FIG. 1 shows the principle of a differential system for a power trainusing the example of a pump. Here, the driven machine 1 is thesymbolically-shown rotor of a pump, which is driven by a drive machine 4via a drive shaft 2 and a differential gear 7 to 9. The drive machine 4is preferably a medium-voltage three-phase machine, which is connectedto a power system 12, which in the illustrated example based on amedium-voltage three-phase machine is a medium-voltage power system. Thechosen voltage level depends on the application and mainly the powerlevel of the drive machine 4 and can have any desired voltage level,without influence on the basic function of the system according to theinvention. According to the number of pole pairs of the drive machine 4,there is a design-specific working speed range. The working speed rangeis that speed range in which the drive machine 4 can deliver a definedor desired or required torque and in which the drive machine 4 in thecase of an electrical drive machine can be synchronized with the powersystem 12, or in the case of an internal combustion engine can bestarted or operated. A planetary carrier 7 of the differential gear isconnected to the drive shaft 2, the drive machine 4 is connected to aninternal gear 8, and a sun gear 9 of the differential gear is connectedto a differential drive 5. The differential drive 5 is preferably athree-phase machine and in particular an asynchronous machine or apermanent magnet-excited synchronous machine.

Instead of the differential drive 5, a hydrostatic actuating gear canalso be used. Here, the differential drive 5 is replaced by ahydrostatic pump/motor combination that is connected to a pressure lineand that are both adjustable preferably in the flow volume. Thus, as inthe case of a variable-speed electrical differential drive 5, the speedscan be adjusted.

The core of the differential system in this embodiment is thus a simpleplanetary gear stage with three drives and power take-offs, one powertake-off being connected to the drive shaft 2 of the driven machine 1, afirst drive being connected to the drive machine 4 and a second drivebeing connected to the differential drive 5.

In order to be able to optimally match the speed range of the system, amatching gear 10 is implemented between the planetary carrier 7 and thedriven machine 1. Alternatively to the illustrated spur gear stage, thematching gear 10 can be designed, for example, also multistage or astoothed belt or chain drive and/or can be combined with a planetary gearstage or a bevel gear stage. With the matching gear 10, an axial offsetcan, moreover, be implemented for the driven machine 1 that enables acoaxial arrangement of the differential drive 5 and of the drive machine4. Electrically, the differential drive 5 is linked to the power system12 by means of a preferably low-voltage converter 6 and—if necessary—atransformer 11. An important advantage of this concept is that the drivemachine 4 can be linked directly, i.e., without complex powerelectronics, to the power system 12. The equalization between variablerotor speed and fixed speed of the power system-linked drive machine 4is implemented by the variable-speed differential drive 5.

The torque equation for the differential system is the following:

Torque_(differential drive)=torque_(drive shaft)*y/x.

The size factor y/x is a measurement of the transmission ratios in thedifferential gear 3 and in the matching gear 10. The torques on thepower take-offs and drives are proportional to one another, as a resultof which the differential drive 5 can control the torque in the entirepower train. The power of the differential drive 5 is essentiallyproportional to the product from the percentage deviation of the speedof the driven machine 1 from its base speed, multiplied by the driveshaft output. In this case, the base speed is that speed that is set onthe driven machine 1 when the differential drive 5 has a speed equal tozero. Accordingly, a large working speed range of the driven machine 1requires corresponding large dimensioning of the differential drive 5.If the differential drive 5 has, for example, a nominal output ofroughly 20% of the total system output (nominal output of the drivenmachine), this means, using a typical so-called field weakening regionof the differential drive 5, that on the driven machine 1, minimumworking speeds of roughly 50% of the nominal working speed can beimplemented. This is also why differential drives according to the stateof the art are especially well suited for small working speed ranges,but fundamentally, any working speed range is practicable. It can,however, be established that higher-pole three-phase machines on astandard basis allow generally higher overspeeds in relation to thesynchronous speed; fundamentally, this enables (at the same nominaloutput of the differential drive 5) a greater working speed range of thedriven machine 1 because a larger field weakening region of thedifferential drive 5 is possible.

To be able to start up the differential system from a speed equal tozero, the differential drive 5 is separably connected to the sun gear 9by means of a clutch 25. A synchronization brake 24 acts on the seconddrive of the differential system and therefore on the sun gear 9 andthus on the entire power train. During start-up, in this embodiment of adifferential system, in a first step, the differential drive 5 isdecoupled from the remainder of the differential system by the clutch25. If at this point the drive machine 4 is run up and connected to thepower system 12, the sun gear 9 turns freely at the same time, and nonoticeable torque can build up in the entire power train. Thus, thedriven machine 1 in this case also remains in a low speed range, and thedrive machine 4 can be connected to the power system 12 withoutnoticeable external counter-torque.

As soon as the drive machine 4 is accelerated above a certain speed andthe driven machine 1 is essentially standing still, on the sun gear 9, ahigh speed corresponding to the transmission ratio of the differentialgear is established, which speed is generally above the allowed controlspeed range of the differential drive 5. The control speed range is thespeed range in which the differential drive 5 works in order to be ableto implement the working speed range of the driven machine 1. Thecontrol speed range is determined mainly by the voltage, current andspeed boundaries that have been specified by the manufacturer.

The differential drive 5 in this embodiment cannot be connected to thesun gear 9 in this phase. In a further step, therefore, by means of thesynchronization brake 24, the second drive of the differential system,which drive is connected to the sun gear 9, is slowed to a speed thatlies in the control speed range of the differential drive 5. Dependingon the implemented braking system 24 and the demands on the power train,this can take place both speed/torque-controlled and also -uncontrolled.Subsequently, the differential-gear-side part of the clutch 25 ispreferably synchronized by means of the differential drive 5 with thespeed of the second drive of the differential system, and then theclutch 25 is engaged.

By actuating the synchronization brake 24 (shown symbolically in FIG. 1as a hydrodynamic brake) and thus by slowing down the second drive ofthe differential system, the drive shaft 2 is necessarily accelerated,the available torque being determined by the minimum from the brakingforce of the synchronization brake 24 acting on the drive shaft 2, onthe one hand, and the breakdown torque of the drive machine 4, on theother hand.

FIG. 2 shows one embodiment of a differential system according to theinvention that enables an oversynchronous working speed range without amatching gear. This embodiment is used preferably for high-speed drivenmachines. Here, the illustrated power train also has, as in FIG. 1, adriven machine 1, a drive shaft 2, a drive machine 4 and a differentialdrive 5 that are connected to the power take-offs and drives of adifferential gear 3. The differential drive 5 is connected to a powersystem 12 by means of a converter 6 (consisting of preferably motor-sideand power-system-side rectifier and inverter—here shown simplified as aunit) and a transformer 11. The drive machine 4 can be connected to thepower system 12 by means of a switch 23.

Since, in the illustrated example, the driven machine 1 is operated witha speed that is distinctly above the synchronous speed of the drivemachine 4, the drive shaft 2 is connected to the sun gear 13 and thedrive machine 4 is connected to the internal gear 14 by means of aconnection shaft 19. The differential drive 5 can be connected using theplanetary carrier 16 to two or more planetary gears 15. Thus, a speedratio between the drive machine 4 and driven machine 1 of, for example,2.5 to 6.5 can be easily achieved with a planetary gear stage andwithout a matching gear. With, for example, a stepped planetary set,moreover, much higher transmission ratios can be achieved. A steppedplanetary set is characterized in that the planetary gears 15 each havetwo gears that are connected torsionally strong to one another and havedifferent pitch circle diameters, one gear interacting with the sun gearand the second gear interacting with the internal gear.

In FIGS. 1 to 3, 5 and 9 to 12, a pump is shown symbolically by way ofexample as a driven machine 1. The principles described here and for thefollowing figures can, however, also be used in drives for drivenmachines, such as, for example, compressors, fans and conveyor belts,pulverizers, crushers, etc., or energy extraction installations and thelike.

As a flow machine, a pump has a square torque characteristic on whichduring start-up, design-typical breakaway torques from the bearingsystem of the power train elements, etc., are superimposed. This leadsto, first of all, a torque at the level of, for example, 10%-20% of thenominal torque of the driven machine 1 having to be overcome duringstart-up. With increasing speed, then the required driving torque drops(by elimination of the breakaway torque) and a torque is establishedthat rises according to the working speed of the driven machine 1(roughly quadratically) and that at nominal speed reaches the nominaltorque. The described torque characteristic is shown by way of examplein a diagram in FIG. 2 a.

With a speed of the internal gear 14 that is determined by the drivemachine 4 and a speed of the sun gear 13 that is required as dictated byoperation, there is necessarily a speed to be set or a torque to be seton the planetary carrier 16, which can be controlled by the differentialdrive 5.

The planetary carrier 16 can, for example, be designed as one part orwith several parts with components that are connected torsionally strongto one another. Since the torque on the planetary carrier 16 is high, itis advantageous to implement, for example, a transmission stage 17, 18between the planetary carrier 16 and the differential drive 5. A spurgear stage, for example, is recommended for this purpose, the gear 17being connected torsionally strong to the planetary carrier 16 and thegear 18 being connected to the differential drive 5. Alternatively, thetransmission stage can, for example, also be multistage, or can bedesigned as a toothed belt, chain drive, planetary stage or as an anglegear. Instead of the transmission stage 17, 18, transmission gearingthat can be continuously adjusted or adjusted optionally in steps canalso be implemented.

FIG. 2 shows a differential drive 5 with a converter 6. Likewise,several differential drives can drive the planetary carrier 16, withwhich the torque of the transmission stage 17, 18 that is to betransmitted is distributed to these differential drives. In this case,the differential drives can be distributed uniformly or elseasymmetrically over the periphery of the gear 17. Preferably—but notnecessarily—the differential drives in this case are triggered by acommon converter 6, then preferably one differential drive acting as aso-called “master” and the other differential drive(s) acting as (a)so-called “slave(s).” The differential drives can also be triggered byseveral motor-side rectifiers or inverters individually or in groups,these so-called motor-side rectifiers and inverters that are connectedto the differential drives having preferably one common so-called powersystem-side rectifier or inverter that is connected to the power system12 via a transformer 11 and that is joined via a DC intermediatecircuit.

When the system is equipped with several differential drives, thenpreferably only one differential drive 5 is connected to the drivemachine 4 via an auxiliary gear—as shown in FIG. 2. In this case, atleast one second differential drive via planetary carrier 16 andtransmission stage 17, 18 drives the auxiliary gear 20 in addition tothe first differential drive 5. Thus, only one auxiliary gear 20 isnecessary.

An auxiliary gear 20 is connected to the connection shaft 19 andsubsequently to the drive machine 4 or the first drive of thedifferential system. This auxiliary gear 20 can be connected to thedifferential drive 5 by means of a clutch 22 and preferably also drivesa lubricating oil pump 21. The clutch 22 can be positioned fundamentallyanywhere between the differential drive 5 and the first drive of thedifferential system—i.e., also in one that is other than the stage ofthe auxiliary gear 20 nearest the differential drive 5. The clutch 22 ispreferably designed as a claw clutch, a geared clutch, a multiple-diskclutch or as a trip-free mechanism. A trip-free mechanism (also calledan overtaking clutch) is in this case a clutch that acts only in onedirection of rotation. It can also be designed in the form of aself-synchronizing clutch. This is a trip-free mechanism in which thetorque is transmitted via a geared clutch. The drive machine 4 can alsobe connected to an intermediate gear stage of the auxiliary gear 20, theconnection of the auxiliary gear 20 to the first drive being maintained.

The differential drive 5 in the illustrated embodiment is separablyconnected to the transmission stage 17, 18 via a clutch 25. In order tostart up the system, the differential drive 5 is connected to thetransmission stage 17, 18 by engaging the clutch 25 and to the auxiliarygear 20 by engaging the clutch 22. By the differential drive 5 thenbeing run up, thus the driven machine 1 and the drive machine 4accelerate at the same time. In the case in which the clutch 22 isdesigned in the form of a trip-free mechanism, the latter automaticallytransmits the rotary motion of the differential drive 5 to the auxiliarygear 20 or the drive machine 4.

If the drive machine 4 is designed as an asynchronous machine, it ispreferably brought to operating speed, and then the switch 23 is closedand the drive machine 4 is connected to the power system 12. The drivemachine, when it is being connected to the power system 12, only brieflydraws a magnetization current. The latter is higher than the nominalcurrent of the drive machine 4, but is only present for a few powersystem periods and is far below the current that is being set and thatthe drive machine 4 would draw if it is switched to the power systemunder load. This magnetization current if necessary can be additionallyreduced by using different recognized technical methods. Then, theclutch 22 is disengaged and the differential system works in theso-called differential mode. If the clutch 22 is designed as a trip-freemechanism, the connection is automatically broken as soon as the speedof the driving part (differential drive 5) becomes lower than the speedof the part that is to be driven (in FIG. 2, auxiliary gear 20) (comparealso FIG. 4 in this respect). If the drive machine 4 is designed as asynchronous machine, according to recognized rules of technology, it canbe synchronized with the power system and thus can be connected to thepower system surge-free. The differential drive 5 in this case helps tosynchronize the drive machine 4 to the power system by its being able tocontrol the speed and preferably also the phase angle of the drivemachine 4 and to synchronize with the power system 12.

If the drive machine 4 is an internal combustion engine, it can bestarted with support of the differential drive 5.

In the case of a malfunction (for example, a power system failure), inthe worst case both the drive machine 4 and also the driven machine 1would run down in an uncontrolled manner. In order to protect thedifferential drive 5 operating in the differential mode againstoverspeed in such a case, either a brake 26 that acts on the seconddrive of the differential system and/or a brake 27 that acts directly onthe differential drive 5 can be used. An alternative approach is todisengage the clutch 25 and in this way to separate the differentialdrive 5 from the remaining differential system.

If the clutch 22 is designed as a trip-free mechanism, its connection isautomatically activated as soon as the speed of the driving part(auxiliary gear 20) becomes lower than the speed of the part to bedriven (differential drive 5), as a result of which an overspeed of thedifferential drive 5 is automatically prevented. Thus, when using atrip-free mechanism as the clutch 22 for the operating modes “start up”and “differential operation” or “malfunction,” neither the clutch 25 northe brakes 26 and 27 are necessary.

If the clutch 22 is designed as a multiple-disk clutch, in the case of amalfunction, it is preferably then activated when the speed differencebetween the output shaft of the auxiliary gear 20 and the differentialdrive 5 is a minimum (ideally at a speed difference of roughly zero).

In another embodiment of the invention, the brake 26 can also be used tobrake the second drive of the differential system during the describedstart-up process in order to avoid an isochronous acceleration of theplanetary carrier 16. Here, the clutch 22 remains engaged and the clutch25 disengaged. Thus, the driven machine 1 can be operated away from aworking speed equal to zero. The maximum attainable drive output for thedriven machine 1 is, however, limited according to the output capacityof the differential drive 5. However, since operation, for example, of aboiler water feed pump also comprises operating modes with a low speed(lower than the attainable working speed in the differential mode) andlow output or else maintenance-dictated start-ups, they can beimplemented by this embodiment.

A similar result is achieved by braking the first drive with a brake (inthe case of FIG. 2, for example, with a brake 28 on the drive machine4). The clutch 25 in this application is engaged and the clutch 22disengaged. Thus, with the internal gear 14 at a standstill, theplanetary carrier 16 and subsequently the driven machine 1 can be drivenwith the differential drive 5. Another application for such a brake 28is to slow down the drive machine 4 in parallel to the driven machine 1in the case of a malfunction in order to prevent an overspeed on thedifferential drive 5.

As FIG. 1 and FIG. 2 show, in a differential system, the first andsecond drives and the power take-off can be alternatively connected toan internal gear or a planetary carrier or a sun gear. In anothervariant according to the invention, the differential drive 5 isconnected to the internal gear 14, the drive machine 4 is connected tothe planetary carrier 16, and the driven machine 1 is connected to thesun gear 13. Other alternative combinations are likewise encompassed bythe invention. The configuration that is shown in FIG. 2 shows oneembodiment with which high speeds on the driven machine 1 can be easilyand economically achieved. One exemplary configuration in which thedriven machine 1 is connected to the internal gear 14, the drive machine4 is connected to the sun gear 13 and the differential drive 5 isconnected to the planetary carrier 16 is one possible variant embodimentfor gearing down.

FIG. 3 shows another embodiment of a differential system according tothe invention for high-speed drives. The differential system isstructured fundamentally the same as described in FIG. 2. In contrast toFIG. 2, the transmission stage 29 is shown as a bevel gear transmissionstage. Thus, the axis of rotation of the differential drive 5 isarranged with an angular offset to the axis of rotation of the drivemachine 4 and the driven machine 1. This results in that an auxiliarygear 30 can also be designed as an angle gear. With the angular offset,the result is that the axial distance between the differential drive 5and the driven machine 1 is increased and in this way, the drivenmachine 1 can be moved nearer the differential system. Likewise, thedifferential drive 5 can be located minor-inverted in the direction ofthe drive machine 4 (compare FIG. 2 and FIG. 5) and thus the drivemachine 4 can be moved nearer the differential system.

The auxiliary gear 30 can preferably be designed in the same manner asthe auxiliary gear 20 such that (a) the direction of rotation of thedriven machine 1 and the drive machine 4 is opposite and (b) the drivemachine 4 preferably reaches its operating speed as soon as thedifferential drive 5 enters the region of its output limit.

The auxiliary gear 30 can be connected to the differential drive 5 bymeans of a clutch 31 and preferably also drives a lubricating oil pump21. The clutch 31 can be positioned anywhere in the path between thedifferential drive 5 and the connection shaft 19, but is preferablylocated between the lubricating oil pump 21 and the differential drive 5to ensure emergency operation of the lubricating system. If thedifferential drive 5 is located minor-inverted to the direction of thedrive machine 4, the first gear of the auxiliary gear 30 runs, forexample, with a coupling capacity on the connection shaft between thedifferential drive 5 and the second drive of the differential system(compare FIGS. 2 and 5).

Fundamentally, the same applies to the execution and functions of theclutch 31 as to the clutch 22. The clutch 22, 31 can, moreover, also bedesigned as a hydrodynamic clutch/torque converter withadditional/integrated blocking function and thus can also be used as anemergency braking system by its being engaged as soon as a malfunctionoccurs in the power train in the differential mode, and the differentialdrive 5 can be protected against overspeed (compare correspondingexplanations to FIG. 2). Alternatively (or in addition), for example, abrake 27 that acts directly on the differential drive 5 can also beused. Fundamentally, according to the invention, however, any type ofclutch can be used.

The clutch 34 that is shown in FIG. 3 is used first of all also likeclutches 32 and 33 for connection of the driven machine 1, drive machine4 and differential drive 5 to the transmission part of the differentialsystem. If the use of a simple and economical clutch 31 is preferred,the clutch 34, as already described for FIG. 2, can be made detachablein operation (if necessary also with automatic disengagement atoverspeed) in order to separate the differential drive 5—in case, forexample, of a malfunction—from the second drive of the differentialsystem. Thus, the brake 27 is also no longer fundamentally necessary.Alternatively, as already stated, instead of the clutch 31, a trip-freemechanism can be used that prevents an overspeed on the differentialdrive 5 in the event of a malfunction. This becomes possible in that incase of a fault in the differential mode (operating mode II), the speedsof the driven machine 1 and of the drive machine 4 always proceed in thedirection of “lowest working speed” and thus the required free-runningdirection is defined accordingly.

The differential system is started up and operated up to its nominaloperating point in three phases, as is explained with respect to FIG. 3.These three phases are the following:

Phase 1: The differential drive 5 is connected to the second drive ofthe differential system and is additionally connected to the first drive(incl. connecting shaft 19 and drive machine 4) of the differentialsystem (in the case of a trip-free mechanism, it is automaticallyactivated) by engaging the clutch 31 by means of the auxiliary gear 30.Then, the differential drive 5 is accelerated, and the driven machine 1begins to work. Depending on the torque characteristic of the drivenmachine 1 (plus a so-called booster pump 69 that may be connected to thepower train) and on the output of the differential drive 5, in thisoperating mode I preferably a continuously adjustable working speed fromzero up to, for example, roughly 40%-50% of the nominal working speed ofthe driven machine 1 can be implemented. The power train is defined hereas the entire drive train between the drive shaft 2 and the drivemachine 4. The drive machine 4 remains in this operating mode Iseparated from the power system.

The transmission ratios of the gears 3, 29 and 30 that are active inthis case are chosen such that the drive machine 4 reaches its operatingspeed as soon as the differential drive 5 enters the region of its powerlimit. That is to say, the differential drive 5 is designed such that it(a) can overcome the inherent breakaway torques of a power train and (b)in the operating mode I, a working speed is reached that lies in theregion of a working speed that is as low as possible and that can beachieved in the differential mode (operating mode II). Preferably, amore or less large overlap of the working speed ranges of operatingmodes I and II is allowed, i.a., in favor of control hysteresis for thetransition between operating modes I and II.

If the intention is to design the differential drive 5 to be as small aspossible in terms of power, a working speed gap between operating modesI and II can also be provided. Here, however, when switching overbetween operating modes I and II, sudden torque and speed changes mustbe tolerated that can be equalized preferably by control engineering orelse with dampers and/or clutches and/or hydrodynamic torque converterswith additional/integrated blocking function—for example as clutch 31.If there is a working speed gap between operating mode I and operatingmode II, the differential drive 5, as described above, cannot acceleratethe drive machine 4 to its operating speed. The drive machine 4 is thenswitched to the power system 12 with a speed lower than its synchronousspeed; this leads to corresponding current and torque surges. They are,however, smaller than if the drive machine 4 with a speed equal to zerois switched to the power system 12. The differential drive 5 isseparated from the auxiliary gear in doing so, while the drive machineis being switched to the power system 12 (in the case of a trip-freemechanism, it is automatically deactivated) and “generates” a reactiontorque on the second drive of the differential system.

The differential drive 5 in any case works as a motor in this firstphase (operating mode I)—i.e., it takes power from the power system.

Phase 2: As soon as the drive machine 4 reaches its operating speed, asalready described for FIG. 2, it is synchronized with the power system12 and the switch 23 is closed.

Since the differential drive 5 works as a generator in the lower workingspeed range of operating mode II—i.e., it delivers power to the powersystem—in the next step, the torque of the differential drive 5 isadjusted from the motor mode that is required for operating mode Ito thegenerator mode that is necessary first of all for operating mode II. Inthis way, the drive machine 4 is continuously more heavily loaded untilthe differential system preferably enters the lower region of theworking speed range of operating mode II.

In order to keep system loads as small as possible, the transition frommotor mode into generator mode of the differential drive takes placepreferably attenuated, i.e., not suddenly.

Phase 3: As soon as the differential system has reached the operatingpoint that was described for phase 2 in the lower working speed range ofthe operating mode II, the differential drive 5 is separated from thefirst drive of the differential system by either the clutch 31 beingdisengaged or, in the case of a trip-free mechanism, the connectionbeing automatically broken (deactivated), as soon as the speed of thedifferential drive becomes lower. At this point, the system is operatingin operating mode II (=differential mode), with which in this thirdphase for the driven machine 1, a maximum torque can be implemented atmaximum drive speed.

In order to switch the differential system over from operating mode IIto operating mode I—for example to turn off the driven machine 1 or fora smaller delivery rate—preferably the following sequence isrecommended:

First, the lower region of the working speed range of operating mode IIis triggered. After preferable synchronization of the two clutch halves(by means of speed control of the differential drive 5), the clutch 31is engaged (if not executed as a trip-free mechanism). As the next step,the torque of the differential drive 5 is adjusted from the generatormode required for operating mode II into the motor mode that is requiredfor operating mode I. In this way, the drive machine 4 is continuouslyrelieved until it no longer delivers torque. By the switch 23 then beingopened, the drive machine 4 can be smoothly separated from the powersystem 12. In the case of the execution of the clutch 22, 31 as atrip-free mechanism, it is automatically activated in this case. Thedifferential system at this point is working in operating mode I and canthus be operated up to a working speed equal to zero.

FIG. 4 shows on a dimensionless time axis the behavior of the torque andthe speed of the driven machine 1, the drive machine 4, the differentialdrive 5 and the clutch 22, 31 during the phases that were described forFIG. 3.

Phase 1: The complete differential system is at time T0. As soon as thedifferential drive 5 begins to turn, the driven machine 1 and the drivemachine 4 also accelerate until the latter reaches its operatingspeed—in FIG. 4 labelled T1. The differential system works in operatingmode I between time tags T0 and T1.

Phase 2: In the next step, the drive machine 4 that is working unloadedup to this instant is synchronized with the power system 12, and theswitch 23 is closed at time T2.

Thereupon in the following step (between T2 and T3), the torque of thedifferential drive 5 is adjusted from motor mode to generator mode (thetorque of the differential drive 5 changes the direction). In this way,the drive machine 4 is continuously more heavily loaded (the torque ofthe drive machine 4 rises) until the differential system preferablyreaches one of the lower operating points of the working speed range ofthe operating mode II. By the resulting new load distribution in thedifferential system, the torque flowing originally via the clutch 22, 31is adjusted toward zero and the clutch 22, 31 is disengaged ordeactivated automatically in the case of a trip-free mechanism. At timeT4, the phase 2 is thus completed.

The speeds for the drives and power take-offs of the differential systemin phase 2 preferably remain essentially constant, but due tooperation-dictated demands on the driven machine 1 or on thesynchronization process of the drive machine 4, they can also vary. Inthis respect, overlapping of the working speeds of operating modes I andII is advantageous since in this way, possible speed fluctuations thatoccur between times T1 and T2 can be corrected and thus the drivemachine 4 can be smoothly connected to the power system 12.

Phase 3: The differential system at this point works between times T4and T6 in operating mode II (=differential mode). In doing so, theregion between T4 and T5 shows a partial load range in which the systemoutput is variably adjusted until it remains between T5 and T6, by wayof example at nominal output with constant nominal torque and constantnominal speed (shown in FIG. 4, therefore, as a constant line). In therange between T4 and T5, the differential drive 5 changes from thegenerator mode to the motor mode; this becomes apparent in its speed(“differential drive” speed).

Operation of the differential system in operating mode II with a speedhigher than nominal speed is fundamentally possible, the differentialdrive 5 then having to be operated in the field weakening region. Indoing so, its torque is available only to a limited degree according tothe known rules of engineering.

The speed of the drive machine 4 (“drive machine” speed) remainsessentially constant in the operating mode II in the case of athree-phase machine.

If the clutch 22 or 31 is designed as a trip-free mechanism,activation/deactivation of the clutch 22, 31 is accomplishedautomatically, with which a flowing transition between the describedphases/operating modes becomes possible.

The time relations of the time axis in FIG. 4 can be configuredindividually and depend on the design criteria of the differentialsystem or on the operating demands.

The described operating concept also applies analogously to a generatormode of, for example, an energy extraction installation. In the case ofusing the system according to the invention in an energy extractioninstallation, the driven machine 1 is, for example, a wind powerinstallation or a water turbine, and the drive machine 4 is anelectrical machine that works essentially in the generator mode.Accordingly, the power flow is turned around in the entire drive traincompared to the representations in FIG. 1 to FIG. 12 and theirdescription. This also applies to, i.a., the control of the torquedirection of the differential drive 5 between T2 and T3, which controlis described here in FIG. 4.

If the differential system for a so-called pump turbine (driven machineis operating at times as a turbine and at times as a pump) is used, botha generator mode (turbine) and also a motor mode (pump) can beimplemented with the system according to the invention, switching fromone operating mode into the other being continuously possible. Thetransition from one operating mode (turbine) into the other (pump) inthis case takes place preferably at time TO.

Fundamentally, the concept described here can also be expanded accordingto the functions and variant embodiments described in FIGS. 2 to 12.

FIG. 5 shows one embodiment of a differential system according to theinvention for preferably slow-running drives. The principle derives fromthe explanations for FIGS. 1, 2 and 3 and can also be used forfast-running drives. The major difference from the concept according toFIGS. 2 and 3 is that the differential drive 5 is connected to the sungear 9 as the second drive of the differential system (instead of theplanetary carrier 16 in FIGS. 2 and 3), and the driven machine 1 isconnected to the planetary carrier 7 (instead of the sun gear 13 inFIGS. 2 and 3).

The differential drive 5 can be connected to the auxiliary gear 20 bymeans of a clutch 22 and preferably also drives a lubricating oil pump21. The clutch 22 can be positioned anywhere in the path between thedifferential drive 5 and the connection shaft 19, but is preferablylocated between the lubricating oil pump 21 and the differential drive 5to ensure emergency operation of the lubricating system.

FIG. 6 shows another embodiment according to the invention, in which adifferential drive 5 can be connected to the second drive and the powertake-off of a differential system. In this embodiment, the differentialdrive 5 is, on the one hand, connected to the second drive of thedifferential system and, on the other hand, can be connected by means ofa clutch 22 and via an auxiliary gear 61 to the power take-off of thedifferential system or the drive shaft 2. Fundamentally, the sameapplies as what was already described for FIGS. 2 to 5, only that thedifferential drive 5 drives both the drive shaft 2 and also the drivemachine 4 via the planetary carrier 7 and the internal gear 8. There isa matching gear stage 60 in FIG. 6 for optimizing the speed controlrange of the differential drive 5.

FIG. 7 shows another embodiment according to the invention, in which adifferential drive 5 of a differential system is connected to the seconddrive and can be connected to the power take-off In contrast to theembodiment according to FIG. 6, here the second drive is connected to aninternal gear 63, the first drive is connected to a planetary carrier 64and the power take-off is connected to a sun gear 65. Accordingly, thedifferential drive 5 controls the speed of the drive shaft 2 via atransmission stage 66 and the externally toothed internal gear 63. Forstarting up, the differential drive 5 can be connected by means of theclutch 31 and an auxiliary gear 62 to the power take-off of thedifferential system. For operationally necessary braking processes,there is a brake 67 (in the illustrated embodiment shown symbolically asa disk brake), which is positioned in the region of the drive shaft ofthe drive machine 4, the brake shoes being connected to the drivemachine 4 and the brake disk preferably to the clutch 33. If the clutch33 is designed with overload protection (for example, a torque limiter),it should preferably be watched that this overload protection not lie inthe primary load path of the braking torque in order thus not to limit abraking torque that can be transferred at maximum with it. The primaryload path is in this case that path over which most of the brakingtorque of the brake 67 flows. One major advantage for the describedpositioning of the brake 67 on the drive machine 4 is that with it, thebearing of the first drive of the differential system remains free ofpossibly active transverse forces (due to non-uniformly acting brakingforces).

FIG. 8 shows another embodiment according to the invention, in which adifferential drive 5 of a differential system is connected to the seconddrive via an externally toothed internal gear 63 and can be connected tothe first drive via the clutch 22 and auxiliary gear 68.

The embodiments according to FIGS. 6, 7 and 8 are especially well suitedfor use in energy extraction installations such as, for example, windpower plants as a driven machine 1. In this case, the drive machine 4 isan electrical machine, which works essentially in the generator mode.Accordingly, the power flow in the entire drive train is turned around(compare in this regard also the explanations for FIG. 4). Thedifferential system is in this case preferably a part of a so-calledprimary gearing, the drive shaft 2 in most cases here being connected tothe other gear stages of this primary gearing in order to achieve a lowspeed that is necessary for the driven machine at correspondingly hightorque.

FIG. 9 shows another embodiment according to the invention, in which thepower take-off can be connected to the first drive of a differentialsystem. In this figure, the differential drive 5 is connected to thesecond drive, on the one hand, and, on the other hand, the powertake-off of the differential system or, for example, the drive shaft 2can be connected via an auxiliary gear 70 by means of the clutch 31 tothe first drive of the differential system or subsequently the drivemachine 4. Fundamentally, the same applies as already described forFIGS. 2 to 8, only that the differential drive 5 in operating mode Idrives the drive machine 4 via the power take-off of the differentialsystem or in the illustrated variant embodiment via the drive shaft 2 inaddition.

FIG. 10 shows another embodiment according to the invention, in whichthe differential drive 5 can be connected to the first drive of thedifferential system via the second drive, transmission gearing 41 and anauxiliary gear 42.

FIG. 11 shows one embodiment of the differential system according to theinvention with a so-called positive gear (also called an epicyclic geartransmission). Here, the drive shaft 19 of the first drive of thedifferential system is connected to a first sun gear 44, and the drivenmachine 1 is connected to a second sun gear 45. A planetary carrier 46is equipped with two or more step planets 47, 48. Step planets arecharacterized by the planet gears each having two gears 47, 48 that areconnected torsionally strong to one another and that have differentpitch circle diameters. In the illustrated embodiment of the invention,the gear 48 interacts with the sun gear 44, and the gear 47 interactswith the sun gear 45. The differential drive 5 drives the planetarycarrier 46 with variable speed. To implement the operating mode I, theplanetary carrier 46 can be connected via a transmission stage 49 and anauxiliary gear 50 to the first drive of the differential system or thedrive machine 4. The directions of rotation of the drive machine 4 andthe driven machine 1 are the same here, and the transmission stage 49 incombination with the auxiliary gear 50 reverses the direction ofrotation relative to the planetary carrier 46. The illustratedembodiment of a differential system in the form of a positive gearallows small transmission ratios between the drive machine 4 and thedriven machine 1 and can also be economically produced due to theabsence of internal gears.

FIG. 12 shows another embodiment of the differential system according tothe invention in the form of a positive gear. Fundamentally, itsoperation derives from the comments on FIG. 11. In this embodiment,however, the auxiliary gear 52 can be connected to the transmission gear51. In another embodiment according to the invention, the differentialdrive 5 is connected directly to the shaft 55.

As FIGS. 2 to 12 show by way of example, there is a host ofpossibilities according to the invention for implementing the operationof starting-up according to the invention. Fundamentally, it is always amatter of bridging the differential system, for example by means of anauxiliary gear 20, 30, 42, 50, 52, 53, 61, 62, 68, 70, so that the drivemachine 4 reaches its operating speed as soon as the driven machine 1reaches, for example, a lower working speed in the operating mode II. Amore or less large overlap of the working speed range of operating modesI and II or a working speed gap can, however, be present, as explained.However, according to the invention in all embodiments, the drivemachine 4 and the driven machine 1 are accelerated in parallel by meansof the differential drive 5.

FIG. 13 shows another embodiment of a differential system according tothe invention for an energy extraction installation. In the case ofusing the system according to the invention in an energy extractioninstallation, the drive machine 42 is an electrical machine that worksessentially in the generator mode—preferably a separately-excitedmedium-voltage synchronous machine (see also explanations to FIGS. 4 and8).

The driven machine 38 (for example, the rotor of a wind power plant) inthis case drives the planetary carrier of a differential stage 40 viathe primary gearing 39. The drive machine that was described inconjunction with FIGS. 1 to 12 is thus operated as a generator 42 in theworking operation range. A differential drive 5 that is connected to thepower system 12 via the converter 6 and the transformer 11 is connectedby means of the shaft 35 (which is routed coaxially in a rotor hollowshaft 43 of the generator 42) to the second drive of the differentialgear 40. The differential drive 5 can be connected to the rotor shaft 43of the drive machine 42 by means of an auxiliary gear 53 and the clutch54, the planetary carrier of the auxiliary gear 53 being connectedtorsionally strong to the housing of the generator 42 or beingintegrated into it. Fundamentally, the same applies to the execution ofthe clutch 54 as to the clutch 22, 31. The auxiliary gear 53 that isshown schematically as a planetary stage can also be replaced byone/several spur gear stage(s) or bevel gear stage(s). This applies inparticular if according to AT 511 720 A, the differential system isdesigned with several differential drives that are connected via a spurgear stage. Fundamentally, however, any type of gearing or belt drivesand the like can be used.

Instead of the differential drive 5, a hydrostatic actuating gear can beused. Here, the differential drive 5 and the converter 6 are replaced bya two-part or multiple-part hydrostatic pump/motor combination, which isconnected to a pressure line and which is preferably adjustable in theflow volume. Thus, as in the case of a variable-speed electricaldifferential drive, the speeds can be adjusted. In doing so, a part ofthe pump/motor combination is preferably connected to the drive shaft 2,and/or by means of an electrical drive at least occasionally connectedto the power system 12, and/or a part of the pump/motor combination isdriven at times by some other drive unit.

This variant embodiment can also be used analogously as a differentialdrive when using a hydrodynamic torque converter.

The system according to the invention can also be used to operate thedrive machine 4 or the generator 42 in the so-called phase shift mode.That is to say, the drive machine either as a motor 4 or as a generator42 can deliver or draw reactive current into or out of the power system12 without the driven machine 1 being operated. In doing so, the drivemachine 4 or 42 is connected and synchronized preferably by means of thedifferential drive 5 only to the power system 12, and then thedifferential drive 5 is separated from the drive machine 4, 42preferably by disengaging the clutch 22, 31, 54 without executing theother steps of the described start-up process. This takes place onlywhen the driven machine 1 must take up operation.

1-42. (canceled)
 43. Power train with a drive shaft (2) of a drivenmachine (1, 38), with a drive machine (4, 42) and with a differentialgear (3, 7 to 9, 40) with three drives and power take-offs, one powertake-off being able to be connected to the drive shaft (2), a firstdrive being able to be connected to a drive machine (4, 42) and a seconddrive being able to be connected to a differential drive (5), whereinone drive can be simultaneously connected to the other drive or to thepower take-off.
 44. Power train according to claim 43, wherein the drivecan be connected by means of an auxiliary gear (20, 30, 42, 50, 52, 53,61, 62, 68, 70) to the other drive or to the power take-off.
 45. Powertrain according to claim 43, wherein the differential drive (5) can beconnected at the same time, both to the first drive or the powertake-off, as well as to the second drive.
 46. Power train according toclaim 45, wherein the differential drive (5) can be connected to thesecond drive, and the second drive can be connected at the same time tothe first drive.
 47. Power train according to claim 43, wherein thedifferential drive (5) can be connected to the first and/or second driveand/or the power take-off via a clutch (22, 31, 54), and the clutch (22,31, 54) is a claw clutch, geared clutch, trip-free mechanism ormultiple-disk clutch.
 48. Power train according to claim 43, wherein thesecond drive is connected to a brake (26).
 49. Power train according toclaim 43, wherein the first drive is connected to a brake (28). 50.Power train according to claim 43, wherein the driven machine (1) is apump, a compressor, fan, conveyor belt, crusher or a pulverizer. 51.Power train according to claim 43, wherein the driven machine (38) is anenergy extraction installation, in particular a wind power plant, awater power plant or marine current plant.
 52. Method for starting up apower train with a drive shaft (2) of a driven machine (1, 38), with adrive machine (4, 42) and with a differential gear (3, 7 to 9, 40) withthree drives and power take-offs, one power take-off being able to beconnected to the drive shaft (2), a first drive being able to beconnected to the drive machine (4, 42) and a second drive being able tobe connected to a differential drive (5), wherein the drive machine (4,42) is started up from a speed of zero or roughly zero, while one driveis connected at the same time to the other drive or to the powertake-off.
 53. Method according to claim 52, wherein the drive machine(4, 42) is started up from a speed of zero or roughly zero, while thedifferential drive (5) is connected at the same time, both to the firstdrive or the power take-off, as well as to the second drive.
 54. Methodaccording to claim 52, wherein the drive machine (4, 42) is anelectrical machine and in this phase is separated from the power system(12).
 55. Method according to claim 52, wherein the differential drive(5) works in the motor mode and at the same time, both drives the firstdrive or the power take-off, and also the second drive.
 56. Methodaccording to claim 52, wherein in this phase, the driven machine isaccelerated to a speed range of up to roughly 40%-50% of the workingnominal speed of the driven machine (1).
 57. Method according to claim52, wherein the drive machine (4, 42) is subsequently synchronized andconnected to a power system (12).
 58. Method according to claim 57,wherein by means of the differential drive (5), the speed and inparticular the phase angle of the electrical machine (4, 42) issynchronized to the power system (12).
 59. Method according to claim 57,wherein the differential drive (5) changes from the motor mode to thegenerator mode after synchronization of the drive machine (4, 42). 60.Method according to claim 52, wherein subsequently, the connectionbetween the drive and the other drive or the power take-off isinterrupted.
 61. Method according to claim 52, wherein the second driveis braked or blocked while it is separated from the differential drive(5).
 62. Method according to claim 52, wherein the drive machine (4, 42)essentially reaches its operating speed as soon as the differentialdrive (5) enters the region of its output limit.
 63. Method according toclaim 52, wherein the first drive is braked or blocked with a brake (28)for operation of the driven machine in the low speed range, while thedifferential drive (5) drives the second drive.
 64. Method according toclaim 52, wherein the second drive is braked or blocked with a brake(26) for operation of the driven machine in the low speed range, whilethe differential drive (5) drives the first drive.
 65. Method accordingto claim 52, wherein in the event of a malfunction, the differentialdrive (5) is connected to the first and second drive or power take-off.